CdTe crystal or CdZnTe crystal and method for preparing the same

Abstract

An object of the present invention is to reduce the etch pit density (EPD) and the full-width-half-maximum (FWHM) value of the double crystal X-ray rocking curve, and to provide a CdTe crystal or a CdZnTe crystal which does not include deposits having Cd or Te and the process for producing the same. After a CdTe crystal or a CdZnTe crystal was grown, while the temperature of the crystal is from 700 to 1050° C., the Cd pressure is adjusted so as to keep the stoichiometry of the crystal at the above temperature. The crystal is left for time t which is determined so that each of a diameter L(r) of the crystal and a length L(z) thereof satisfies the following equation 1:Then, when the crystal is cooled, the temperature of the crystal is decreased within a range in which the temperature of the crystal and that of a Cd reservoir satisfy the following equation 2:

What is claimed is:  
     
       1. A CdTe crystal or a CdZnTe crystal, wherein deposits comprising Te or Cd are not observable by an IR microscope, an etch pit density (EPD) of the crystal is not more than 3×10 4  cm −2 , and a full-width-half-maximum (FWHM) of a double crystal X-ray rocking curve of the crystal is not more than 20s. 
     
     
       2. A CdTe crystal or a CdZnTe crystal as claimed in claim  1 , wherein the crystal is an n-type CdTe crystal or an n-type CdZnTe crystal. 
     
     
       3. A CdTe crystal or a CdZnTe crystal as claimed in claim  1 , wherein the crystal is a p-type CdTe crystal or a p-type CdZnTe crystal. 
     
     
       4. A process for producing a CdTe crystal or a CdZnTe crystal as claimed in claim  1 , comprising the steps of 
       growing a CdTe crystal or a CdZnTe crystal,  
       maintaining a temperature of the grown crystal from 700 to 1050° C.,  
       adjusting a Cd pressure so as to maintain a stoichiometry of the crystal at said temperature,  
       maintaining the crystal for time t which is determined so that each of a diameter L(r) of the crystal and a length L(z) of the crystal satisfies the equation  
       
         
             {L ( r ), L ( z ))}/2<{4exp(−1.15 /kT )× t}{fraction ( 1 / 2 )}   
         
       
       wherein k is Boltzmann's constant, T is an absolute temperature, t is time (in seconds), and {4exp(−1.15/kT)×t} ½  is a chemical diffusion distance (in centimeters), and 
       cooling the remaining crystal so that the temperature of the crystal is decreased within a range in which the temperature of the crystal and that of a Cd reservoir satisfy the equation  
       
         
           −288+1.68× T   Cd   <T   CdTe <402+0.76× T   Cd    
         
       
       where T CdTe  is the temperature of the crystal and T Cd  is the temperature of the Cd reservoir. 
     
     
       5. A process for producing a CdTe crystal or a CdZnTe crystal as claimed in claim  4 , wherein the step of growing the CdTe crystal or the CdZnTe crystal is carried out by a vapor pressure (Cd pressure) control method, a VGF method, or an HB method.